Check out this thread and you'll see that you're getting a lot of bang for your gas $$. Can you run regular unleaded in the Titan, or does it say "premium fuel only?"
http://www.nissanforums.com/showthread.php?t=42391
The one disappointment I have had with my truck is that it's gas mileage isn't much better than the Q's. Best I've seen on the truck is about 21MPG. The 2.4L is just labored so much of the time that I think it really is underpowered. The good news is that I only use my truck for the occasional trip to Home Depot or when I just want to give the Q a break, so it's not that bigh of a deal. I get between 17-20 on the Qs, with a lot of mixed driving, so 17.6 sounds about right... actually pretty good with the extra 1.6L of displacement! Several Q guys are waiting for someone to total out a Titan or Armada so we can try dropping one into a 1st gen Q45!
Heath